Process for substrate incorporating component

ABSTRACT

In a process for producing the component-embedded substrate, a first electronic component is connected and fixed onto a first electrode pattern with a conductive bonding material, the first electrode pattern being provided on a first supporting layer. A second supporting layer including a second electrode pattern is press-bonded onto the electronic component-fixed surface of the first supporting layer with a first prepreg therebetween to perform transfer. Then, the first supporting layer and the second supporting layer are separated from the first prepreg. After separation, the first prepreg is cured. A second electronic component is connected and fixed onto the back surface of the second electrode pattern with a conductive bonding material. A third supporting layer including a third electrode pattern is press-bonded onto the second electronic component-fixed surface with a second prepreg therebetween to perform transfer. Then, the third supporting layer is separated from the second prepreg, and the second prepreg is cured. In this manner, the prepregs and electrode patterns are sequentially laminated, thereby reducing the connection resistance between laminated electrode patterns or between an electrode pattern and an electronic component.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for producing a substrateincluding therein an electronic component, such as a semiconductorelement and a chip component.

2. Description of the Related Art

Demands for miniaturization and higher performance of electronic devicesrequire a further reduction in the profile of components having asmaller mounting area. To meet such requirements, a component-embeddedsubstrate is known in which multiple resin layers including asemiconductor element and a chip component therein are laminated.

Patent Document 1 (Japanese Unexamined Patent Application PublicationNo. 2002-76637) discloses a process for producing the component-embeddedsubstrate by press-bonding and transferring a supporting layer includinga component-connected electrode pattern onto one surface of a prepreg,and then laminating the resulting prepreg with another prepreg in whicha component is embedded by press bonding in a single step.

FIG. 8 is an example shown in FIG. 15 in Patent Document 1. In step (a),a prepreg 1501 including via holes 1502 and a supporting layer 1504including an electrode pattern on which electronic components 1510 and1511 are connected are prepared. In step (b), the prepreg 1501 and thesupporting layer 1504 are laminated by press bonding. In step (c), thesupporting layer 1504 is separated to form a wiring layer 1515. In step(d), the wiring layer 1515, another wiring layer 1514 in which anelectronic component 1505 is embedded, wiring layers 1512 and 1513including an electrode pattern 1506 and an interlayer via 1507,respectively, are laminated by press bonding in a single step to form amultilayer component-embedded substrate 1516 as shown in (e).

However, in such a single-step lamination process, at the interlayerbetween the laminated prepregs, an electrode pattern transferred on thesurfaces of the prepregs is only in contact with another electrodepattern or an electronic component to provide an electrical connection.Thus, the connection resistance is disadvantageously increased, whichresults in insufficient connection reliability. Furthermore, since twoelectrode layers are disposed between the laminated prepregs, thebonding strength between the prepregs is low, thus possibly causingdelamination.

To overcome these problems, in FIG. 16 in Patent Document 1, discloses aprocess in which a prepreg defining an adhesive layer including athrough hole is provided between the cured resin layers to ensure theconnection reliability between the electrode patterns or between theelectrode pattern and the electronic component. However, this processdisadvantageously requires an interlayer prepreg including no component.Thus, the thickness of the component-embedded substrate is increased.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide a process for producing a component-embeddedsubstrate having low connection resistance between laminated electrodepatterns or between an electrode pattern and an electronic component,the electrode pattern and the electronic component being laminated, andhaving improved connection reliability.

According to another preferred embodiments of the present invention,when electronic components are connected onto front and back surfaces ofan inner layer electrode, a process is provided for producing acomponent-embedded substrate having improved connection reliabilitybetween the inner layer electrode and the electronic components.

According to a first preferred embodiment of the present invention, aprocess is provided for producing a component-embedded substrate,including the steps of connecting and fixing a first electroniccomponent to a first electrode pattern on a first supporting layer witha conductive bonding material, press-bonding a second supporting layerincluding a second electrode pattern onto the electronic component-fixedsurface of the first supporting layer with a first prepreg therebetweento perform transfer, separating the first supporting layer and thesecond supporting layer from the first prepreg, curing the first prepregbefore or after the separating step, connecting and fixing a secondelectronic component onto the back surface of the second electrodepattern with a conductive bonding material, press-bonding a thirdsupporting layer including a third electrode pattern onto a secondelectronic component-fixed surface with a second prepreg therebetween toperform transfer, separating the third supporting layer from the secondprepreg, and curing the second prepreg before or after the separatingstep, wherein the prepregs and the electrode patterns are sequentiallylaminated.

According to a second preferred embodiment of the present invention, aprocess is provided for producing a component-embedded substrateincluding the steps of connecting and fixing a first electroniccomponent on the surface of an electrode pattern on a supporting layerwith a conductive bonding material, press-bonding a first prepreg ontothe first electronic component-fixed surface of the supporting layer,separating the supporting layer from the first prepreg, curing the firstprepreg before or after the separating step, connecting and fixing asecond electronic component onto the back surface of the electrodepattern with a conductive bonding material, press-bonding a secondprepreg onto the second electronic component-fixed surface, and curingthe second prepreg.

According to a third preferred embodiment of the present invention, aprocess is provided for producing a component-embedded substrateincluding the steps of connecting and fixing a first electroniccomponent onto the surface of a first electrode pattern on a firstsupporting layer with a conductive bonding material, press-bonding asecond supporting layer including a second electrode pattern onto theelectronic component-fixed surface of the first supporting layer with afirst prepreg therebetween to perform transfer, separating the firstsupporting layer and the second supporting layer from the first prepreg,curing the first prepreg before or after the separating step, connectingand fixing a second electronic component onto the back surface of thefirst electrode pattern with a conductive bonding material,press-bonding a third supporting layer including a third electrodepattern onto a second electronic component-fixed surface with a secondprepreg therebetween to perform transfer, separating the thirdsupporting layer from the second prepreg, and curing the second prepregbefore or after the separating step, wherein the prepregs and theelectrode patterns are sequentially laminated.

According to the first preferred embodiment of the present invention, aplurality of layers are not laminated in a single step, but instead, aresequentially laminated. The first electronic component is connected andfixed onto the first electrode pattern with the conductive bondingmaterial. The first electrode pattern is integrally press-bonded to thesecond electrode pattern with the first prepreg therebetween. In thispreferred embodiment, a process for transferring the electrode patternsby forming the electrode patterns on the supporting layers,press-bonding the resulting electrode patterns to the prepregs, and thenperforming separation is preferably used. Next, the second electroniccomponent is connected and fixed onto the back surface of the secondelectrode pattern with the conductive bonding material. The thirdelectrode pattern is press-bonded and transferred onto the resultingsecond electrode pattern with the second prepreg therebetween.

In this manner, by sequentially laminating the prepregs and theelectrode patterns, a component-embedded substrate having a multilayerstructure is produced.

The electrode pattern is connected to the electronic component with theconductive bonding material (solder, a conductive adhesive, a bump, orthe like), thus reducing connection resistance between the electrodepattern and the electronic component and achieving high connectionreliability.

According to the first preferred embodiment, the electrode pattern istransferred to the prepreg. After curing this prepreg, the next prepregis press-bonded simultaneously with the transfer of the electrodepattern to the surface. Consequently, the resulting inner layerelectrode between the prepregs (resin layers) is a single layer and isdifferent from the conventional structure having two inner layerelectrodes. Therefore, it is unnecessary to contact and electricallyconnect the inner layer electrodes to each other. Furthermore, theoccurrence of delamination between the inner layer electrodes isprevented.

The electrode pattern is transferred to the prepreg, and after curingthis prepreg, the next prepreg is laminated. Thus, the first prepreg isnot compressed during every lamination, and no problems, such as thepoor electrical connection of the electrical component embedded in thefirst prepreg or the deformation of the electrode pattern, occur.

Curing of the prepreg may be performed before or after separation of thesupporting layer.

According to the second preferred embodiment of the present invention,when the electronic components are connected onto the front and backsurfaces of the inner layer electrode, the process is provided in whichthe electronic component is connected and fixed onto the surface of theelectrode pattern with the conductive bonding material, this istransferred to the first prepreg, the first prepreg is cured, the secondelectronic component is connected and fixed onto the back surface of theelectrode pattern with the conductive bonding material, and the secondprepreg is press-bonded thereon.

Conventionally, when electronic components are connected onto the frontand back surfaces of an inner layer electrode, the electrodes of theelectronic components must be brought into contact with and electricallyconnected to the inner layer electrode, which results in low conductionreliability and high connection resistance between the componentelectrodes and the inner layer electrode. In contrast, according to thesecond preferred embodiment, not only is lamination sequentiallyperformed one layer at a time, but the second electronic component isalso connected and fixed onto the back surface of the first electrodepattern with the conducive bonding material, the first electrode patternconnecting and fixing the first electronic component on the frontsurface with the conducive bonding material, thus resulting in highconduction reliability and low connection resistance between the innerlayer electrode and the electronic component.

In addition, after curing the first prepreg, the second prepreg ispress-bonded in a similar manner to the first preferred embodiment.Thus, the deviation and the breakage of the electrode patterntransferred to the first prepreg and a poor connection between theelectronic component and the electrode pattern are prevented.Furthermore, the delamination between the prepregs does not occur.

According to the third preferred embodiment, in the step ofpress-bonding the first prepreg and the second prepreg in the processaccording to the second preferred embodiment, a substep of disposing thesupporting layer having the electrode pattern on the surface oppositethe press-bonded surface of the prepreg and then press-bonding thissupporting layer to the prepreg simultaneously with the above-describedpress-bonding step is included, and after the press-bonding substep, thesecond supporting layer is separated from the prepreg to transfer theelectrode pattern to the prepreg.

In the process according to the second preferred embodiment, when theelectrode pattern is provided on the surface opposite the press-bondedsurface of the prepreg, a process of separately forming a thick-filmelectrode pattern or a thin-film electrode pattern after curing theprepreg is provided. This disadvantageously increases the number ofsteps.

Accordingly, in the process according to the third preferred embodiment,by simultaneously transferring the electrode patterns to both of thefront and back surfaces, it is unnecessary to form a new electrodepattern after press-bonding the prepreg. Therefore, the number of stepsis reduced.

According to a fourth preferred embodiment, the process preferablyfurther includes the steps of forming a through hole in the resin layerin the thickness direction after curing the prepreg, and forming aconducting path inside the hole, the conducting path electricallyconnecting the electrode patterns provided on the front surface and theback surface of the resin layer.

Conventionally (in Patent Document 1), a through hole is formed in aprepreg and is then filled with a conducting material. After performinglamination, the prepreg is thermally cured. However, during the thermalcuring, the contraction of the prepreg due to curing may cause adeviation of the position of the electrode pattern being in contact withthe through hole, thus possibly reducing connection reliability.

In contrast, in accordance with the fourth preferred embodiment, aftercuring the prepreg, a hole (a through hole or a via hole) is provided,and a conducting path is formed inside the hole. Therefore, it ispossible to securely connect the hole with the electrode patternswithout any positional deviation of the electrode patterns on the frontand back surfaces of the resin layer.

As a process for forming the conducting path, the inner surface of thehole may be plated. Alternatively, the conducting path may be formed byfilling the inside of the hole with a conducting paste and then curingthe paste.

According to a fifth preferred embodiment, the process preferablyfurther includes the steps of forming the hole connecting the electrodepattern provided on the front surface or the back surface of the resinlayer with the external electrode of the electronic component aftercuring the prepreg, and forming the conducting path inside the hole, theconducting path electrically connecting the electrode pattern with theexternal electrode of the electronic component.

In accordance with the fourth preferred embodiment, the electrodepatterns on the front and back surfaces of the resin layer are connectedto each other. On the other hand, in accordance with the fifth preferredembodiment, one of the electrode patterns is directly connected to theexternal electrode of the electronic component. The wiring resistance ofthe through holes and via holes is higher than that of usual copperwiring. Therefore, the hole desirably has the minimal length. In thiscase, since the length of the hole is reduced by the thickness of thecomponent, the resistance of the conducting path is advantageouslyreduced.

In accordance with a sixth preferred embodiment, the step of curing theprepreg preferably includes a substep of performing temporary curingbefore separating the supporting layer from the prepreg, and performingcomplete curing after separating the supporting layer from the prepreg.

When the supporting layer is separated without curing the prepreg,problems, such as difficulty in the separation of the supporting layeror breakage of the prepreg, may occur because of the adhesion betweenthe prepreg and the supporting layer. In contrast, performing temporarycuring before separating the supporting layer from the prepregfacilitates separation of the supporting layer from the prepreg whiledeformation of the prepreg is prevented.

When the next prepreg is laminated in the temporarily cured state, theprepreg being in the temporarily cured state may be deformed bycompression. Therefore, complete curing should be performed before thelamination of the next prepreg.

When an epoxy resin is used in the prepreg, as the temporary curingconditions, for example, heat treatment should be performed at about120° C. for about 10 to 15 minutes. As the complete curing conditions,heat treatment should be performed at about 170° C. to about 200° C. forabout 1 hour.

In accordance with a seventh preferred embodiment, after curing thesecond prepreg, a step of press-bonding a fourth supporting layer havinga fourth electrode pattern onto the surface of the first prepreg with athird prepreg therebetween to perform transfer, the surface beingopposite to the surface bonded to the second prepreg, a step ofseparating the fourth supporting layer from the third prepreg, andcuring the prepreg before or after the separating step, are preferablyprovided.

When three or more prepregs are laminated, a process of laminating asecond prepreg defining a second layer on a first prepreg defining afirst layer and then laminating a third prepreg defining a third layeron the second layer prepreg is preferable. However, the first resinlayer (prepreg) is warped toward the second layer prepreg by thecontraction of the second layer prepreg during curing. Thus, when thethird layer prepreg is laminated thereon, the resulting laminate isfurther warped by the contraction of the third layer prepreg duringcuring.

Accordingly, in the seventh preferred embodiment, when the second layerprepreg is laminated on the first layer prepreg, the third layer prepregis not laminated on the second layer prepreg, but rather, on the firstlayer prepreg. As a result, the influence of the warpage caused by thecontraction of the second layer prepreg during curing is compensated bythe contraction of the third layer prepreg during curing, therebyresulting in a laminate reduced warpage.

Other features, elements, steps, advantages and characteristics of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments thereof with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a component-embedded substrateproduced by a production process according to a first preferredembodiment of the present invention.

FIG. 2 is a process chart for producing the component-embedded substrateshown in FIG. 1.

FIG. 3 is a process chart for producing the component-embedded substrateaccording to a second preferred embodiment of the present invention.

FIG. 4 is a process chart for producing the component-embedded substrateaccording to a third preferred embodiment of the present invention.

FIG. 5 is a process chart for producing the component-embedded substrateaccording to a fourth preferred embodiment of the present invention.

FIG. 6 is a perspective view of a component-embedded substrate accordingto a fifth preferred embodiment of the present invention.

FIG. 7 is a process chart for producing the component-embedded substrateaccording to a sixth preferred embodiment of the present invention.

FIG. 8 is a process chart for producing a conventionalcomponent-embedded substrate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a component-embedded substrate A produced by a processaccording to a first preferred embodiment of the present invention.

In FIG. 1, reference numerals 1 and 2 represent resin layers definingthe substrate. Patterned outer layer electrodes 3 and 4 are provided onthe front and back surfaces of the resin layers 1 and 2, respectively. Apatterned inner layer electrode 5 is provided between the resin layers 1and 2. An electronic component 6 is connected and fixed onto the innersurface of the outer layer electrode 4, which is provided on the lowerside, with a conductive bonding material 7. An electronic component 8 isconnected and fixed onto the upper surface of the inner layer electrode5 with a conductive bonding material 9. As the conductive bondingmaterials 7 and 9, solder, conducting adhesives, bumps, or othersuitable conductive bonding materials are preferably used. The outerlayer electrode 4, which is provided on the lower side, is appropriatelyconnected to the inner layer electrode 5 through a via hole 10 filledwith a conducting material. The outer layer electrode 3, which isprovided on the upper side, is connected to the inner layer electrode 5through a via hole 11.

The via holes 10 and 11 each have a diameter of, for example, about 100μm to about 500 μm and a length of about 100 μm to about 1,000 μm, andare preferably formed by a laser or by drilling. As a conductingmaterial with which the via holes 10 and 11 are filled, for example, abinder that is composed of glass, a resin, or other suitable binder andthat contains Cu, Ag, Ni, Au, Sn, Zn, Pd, or Pt or a mixture thereofserving as a conductive material is preferably used, the content of theconductive material being about 20% to about 90%.

The outer layer electrodes 3 and 4 and the inner layer electrode 5 areeach made of, for example, a metal thin film having a thickness of about10 μm to about 40 μm. As the electrodes 3, 4, and 5, for example, acopper foil is preferably used. The copper foil may be gold plated, tinplated, or preflux treated.

As the resin layers 1 and 2, for example, an epoxy resin including aninorganic filler is preferably used. The content of the inorganic filleris, for example, about 60% to about 95%. The inorganic filler ispreferably composed of an insulating material, such as SiC, Al₂O₃, orAlN, and preferably has a size of, for example, about 0.1 μm to about 10μm. In this manner, by incorporating the inorganic filler, the linearexpansion coefficient of the prepreg described below is reduced, andthus, the linear expansion coefficient of the prepreg is close to thelinear expansion coefficient of a wiring material defining the electrodepattern and to the linear expansion coefficient of the conductivebonding material. Furthermore, stress applied to a junction duringheating is reduced. Therefore, the reliability of the junction isimproved.

A process for producing the component-embedded substrate A having thestructure described above will be described below according to FIG. 2.This production process corresponds to the first preferred embodiment.

In step (a), an electrode that is made of a copper foil and that isbonded onto a supporting layer 12 is etched to form a circuit pattern 4.The circuit pattern 4 may be directly formed on the supporting layer 12by plating, evaporation, or other suitable method. The supporting layer12 may be formed of, for example, a thin metal plate composed ofstainless steel (SUS) or other suitable material and having a thicknessof, for example, about 1.0 mm.

The conducting adhesive 7 is applied to a predetermined location of theelectrode pattern 4. The electronic component 6 is mounted on theconductive bonding material 7 and is placed in, for example, an oven setat about 120° C. to cure the conductive bonding material 7. With respectto a method of applying the conducting adhesive 7, printing using a meshscreen or a metal mask, dispensing, or other suitable method is used. Inthis case, the conducting adhesive used as the conductive bondingmaterial 7 is thermosetting, and thus, is cured in an oven. When a UVcurable adhesive is used, curing is performed by UV irradiation. When acyanoacrylate adhesive is used, curing is performed with a minute amountof water present on the surface of an adherend. When an anaerobicadhesive is used, curing is performed by blocking air (oxygen).

In step (b), another supporting layer 13 including the electrode pattern5 provided on a surface thereof is press-bonded onto thecomponent-mounted side of the supporting layer 12 with the prepreg 2therebetween. At the same time, the prepreg 2 is temporarily cured. Bythe press-bonding, the electronic component 6 is embedded in the prepreg2, and the electrode patterns 4 and 5 are bonded to the front and backsurfaces of the prepreg 2. As the temporary curing conditions, forexample, heat treatment is preferably performed at about 120° C. forabout 10 to about 15 minutes. The electrode pattern 5 is formed on thesupporting layer 13 by the same process as that for of electrode pattern4. The material and shape of the supporting layer 13 are preferablyidentical to those of the supporting layer 12. In this manner, anelectronic component is not mounted on the surface of the electrodepattern 5 but temporarily fixed.

In step (c), after thermocompression-bonding and curing of the prepreg2, the supporting layers 12 and 13 are separated from the temporarilycured prepreg 2, thereby transferring the electrode patterns 4 and 5onto the front and back surfaces of the prepreg 2. After the separation,the prepreg 2 is completely cured. As the complete curing conditions,for example, heat treatment is preferably performed at about 170° C. toabout 200° C. for about 1 hour.

In step (d), the through hole or via hole 10 is formed in the curedresin layer 2 and is then filled with a conducting material toelectrically connect the front-side electrode pattern 5 to the back-sideelectrode pattern 4. The via hole 10 is formed by a laser or bydrilling. In this manner, since the via hole 10 is formed in the curedresin layer 2, deviations of the connection locations of the via hole 10and the electrode patterns 4 and 5 caused by curing contraction does notoccur, thus resulting in a highly precise connection structure. When theprepreg 2 is cured after separating the supporting layers 12 and 13 fromthe prepreg 2, it is also possible to form the via hole 10 byirradiating the uncured prepreg with a laser.

In step (e), the electronic component 8 is connected and fixed onto theelectrode pattern 5 with the conductive bonding material 9, theelectrode pattern 5 being provided on the front side. Also in this case,a conducting adhesive is used as the conductive bonding material 9. Theconducting adhesive 9 is preferably cured in an oven set at, forexample, about 120° C.

In step (f), another supporting layer 14 including the electrode pattern3 provided on a surface thereof is press-bonded onto the surface of theresin layer 2 with the prepreg 1 therebetween, the surface fixing theelectronic component 8. At the same time, the prepreg 1 is temporarilycured. By press-bonding, the electronic component 8 is embedded in theprepreg 1, and electrode patterns 5 and 3 are bonded onto the front andback surfaces of the prepreg 1. The temporary curing conditions are thesame as those described above. The electrode pattern 3 is preferablyformed on the supporting layer 14 by the same process as that for theelectrode pattern 4. The material and shape of the supporting layer 14are preferably identical to those of the supporting layer 12. In thiscase, an electronic component is not mounted on the outer layerelectrode 3 but may be appropriately connected and fixed using theconductive bonding material.

In step (g), after thermocompression-bonding and curing the prepreg 1,the supporting layer 14 is separated from the temporarily cured prepreg1, thereby transferring the electrode pattern 3 onto the surface of theprepreg 1. After separation, the prepreg is completely cured. Thecomplete curing conditions are the same as those described above.

In step (h), the through hole or via hole 11 is formed in the curedresin layer 1 and is then filled with a conducting material toelectrically connect the electrode pattern 3 with the electrode pattern5.

Steps (a) to (h) are included in the process for producing thecomponent-embedded substrate A having two resin layers 1 and 2. Bysequentially laminating other resin layers on the outer surface of theresin layer 1 or 2, it is also possible to form a component-embeddedsubstrate having a multilayer structure.

As shown in FIG. 2, after connecting the electronic components 6 and 8with the electrode patterns 4 and 5 using the conductive bondingmaterials 7 and 9, the prepregs 2 and 1 are press-bonded, thuspreventing detachment of the electronic components 6 and 8 from theelectrode patterns 4 and 5 during the press-bonding of the prepregs 2and 1, and reducing the connection resistance. Since the electrodepattern 5 interposed between the resin layers 1 and 2 is a single layer,the two resin layers 1 and 2 are securely bonded with the electrodepattern 5 provided therebetween. Therefore, delamination of the resinlayers 1 and 2 from the electrode pattern 5 is eliminated.

FIG. 3 shows a process for producing a component-embedded substrate Baccording to a second preferred embodiment of the present invention.

In step (a), an electrode pattern 21 is formed on a supporting layer 20,and an electronic component 22 is connected and fixed onto the surfaceof the electrode pattern 21 with a conductive bonding material 23. Thesupporting layer 20, the electrode pattern 21, and the conductivebonding material 23 are the same as those in the first preferredembodiment shown in FIGS. 1 and 2. Thus, the descriptions thereof areomitted.

In step (b), another supporting layer 25 is press-bonded onto thecomponent-mounted surface of the supporting layer 20 with a prepreg 24therebetween. At the same time, the prepreg 24 is temporarily cured. Bypress-bonding, the electronic component 22 is embedded in the prepreg24, and the electrode pattern 21 is bonded to the lower surface of theprepreg 24. The temporary curing conditions are preferably the same asthose in the first preferred embodiment.

In step (c), after thermocompression-bonding and curing the prepreg 24,the supporting layers 20 and 25 are separated from the temporarily curedprepreg 24, thereby transferring the electrode pattern 21 to the lowersurface of the prepreg 24. Then, the prepreg 24 is completely cured. Thecomplete curing conditions are preferably the same as those in the firstpreferred embodiment.

In step (d), the cured resin layer 24 is flipped over, and an electroniccomponent 26 is connected and fixed onto the back surface of theelectrode pattern 21 with a conductive bonding material 27.

In step (e), another supporting layer 29 is press-bonded onto thesurface fixing the electronic component 26 with a prepreg 28therebetween. At the same time, the prepreg 28 is temporarily cured. Bypress-bonding, the electronic component 26 is embedded in the prepreg28, and the prepreg 28 is bonded to the electrode pattern 21. Thetemporary curing conditions are the same as those described above.

In step (f), after thermocompression-bonding and curing the prepreg 28,the supporting layer 29 is separated from the temporarily cured prepreg28. After the separation, the prepreg 28 is completely cured. Thecomplete curing conditions are the same as those in the first preferredembodiment.

As described above, the component-embedded substrate B having atwo-layer structure is obtained. Next, electrode patterns are formed onthe front and back surfaces of the resin layers 24 and 28, and the innerlayer electrode 21 is preferably connected to the exterior by providinga through hole or a via hole.

As described above, when the electronic components 22 and 26 areconnected onto the front and back surfaces of one inner layer electrode21, the electronic components 22 and 26 are connected and fixed onto theinner layer electrode 21 with the conductive bonding materials 23 and27, respectively. Thus, the conduction reliability between the innerlayer electrode 21 and the electronic components 22 and 26 is improved,and the connection resistance is reduced.

FIG. 4 shows a process for producing a component-embedded substrate Caccording to a third preferred embodiment of the present invention.

In step (a), an electrode pattern 31 is formed on a supporting layer 30,and an electronic component 32 is connected and fixed onto the surfaceof the electrode pattern 31 with a conductive bonding material 33. Sincethe supporting layer 30, the electrode pattern 31, and the conductivebonding material 33 are identical to those in the first preferredembodiment shown in FIGS. 1 and 2, the descriptions thereof are omitted.

In step (b), another supporting layer 35 including an electrode pattern36 provided on the surface thereof is press-bonded onto thecomponent-mounted surface of the supporting layer 30 with a prepreg 34therebetween. At the same time, the prepreg 34 is temporarily cured. Thetemporary curing conditions are preferably the same as those in thefirst preferred embodiment.

In step (c), after thermocompression-bonding and curing the prepreg 34,the supporting layers 30 and 35 are separated from the temporarily curedprepreg 34. After separation, the prepreg 34 is completely cured. Thecomplete curing conditions are the same as those in the first preferredembodiment.

In step (d), a through hole 37 or a via hole 38 is formed in the curedresin layer 34 and is then filled with a conducting material toelectrically connect the front-side electrode pattern 31 with theback-side electrode pattern 36 and to electrically connect the electrodepattern 36 with the external electrode of the electronic component 32.The via hole 37 or 38 is formed by the same process as that in the firstpreferred embodiment. In this manner, since the electrode pattern 36 iselectrically connected to the external electrode of the electroniccomponent 32 through the via hole 38, the length of the via hole 38 isreduced by the thickness of the electronic component 32, and thus, theresistance of a conducting path is reduced.

In step (e), the cured resin layer 34 is flipped over, and an electroniccomponent 39 is connected and fixed onto the back surface of theelectrode pattern 31 with a conductive bonding material 40.

In step (f), another supporting layer 42 including an electrode pattern43 provided on the surface thereof is press-bonded onto the surfacefixing the electronic component 39 with a prepreg 41 therebetween. Atthe same time, the prepreg 41 is temporarily cured. The temporary curingconditions are the same as those in the first preferred embodiment.

In step (g), after thermocompression-bonding and curing the prepreg 41,the supporting layer 42 is separated from the temporarily cured prepreg41. After the separation, the prepreg 41 is completely cured. Thecomplete curing conditions are the same as those in the first preferredembodiment.

In step (h), a through hole 44 or a via hole 45 is formed in the curedresin layer 41 and is then filled with a conducting material toelectrically connect the front-side electrode pattern 43 with theback-side electrode pattern 31 and to electrically connect the electrodepattern 43 with the external electrode of the electronic component 39.

In this component-embedded substrate C, in the same manner as for thecomponent-embedded substrate B, the electronic components 32 and 39 areconnected and fixed onto the front and back surfaces of one inner layerelectrode 31 with conductive bonding materials 33 and 40. Therefore, theconduction reliability between the inner layer electrode 31 and theelectronic components 32 and 39 is improved, and the connectionresistance is reduced. Furthermore, the outer layer electrodes 36 and 43are simultaneously formed by transfer with the press-bonding of theprepregs 34 and 41. Thus, the steps of forming the outer layerelectrodes 36 and 43 are omitted.

FIG. 5 shows a process for producing a component-embedded substrate Daccording to a fourth preferred embodiment of the present invention.This production process provides an exemplary component-embeddedsubstrate including a shield electrode therein.

In step (a), a shield electrode 55 and an electrode pattern 52 thatincludes an electronic component 53 connected and fixed onto a surfacethereof with a conductive bonding material 54 are transferred onto thefront and back surfaces of a resin layer 51 to prepare a sheet 50. Aprocess for producing this sheet 50 includes the same steps as, forexample, steps (a) to (d) shown in FIG. 2, except that the front-sideelectrode is the shield electrode 55 covering substantially the entirefront surface. The electrode pattern 52 is connected to the shieldelectrode 55 through the via hole 56.

Another supporting layer 58 including an electrode pattern 59 providedon a surface thereof is press-bonded onto the shield electrode 55 of thesheet 50 with a prepreg 57 therebetween. An electronic component 60 isconnected and fixed onto the electrode pattern 59 with a conductivebonding material 61. The prepreg 57 is temporarily cured simultaneouslywith the press-bonding.

In step (b), the supporting layer 58 is separated. In this state, theprepreg 57 is securely bonded and fixed onto the back surface of theshield electrode 55. The electronic component 60 is embedded in theprepreg 57. At the same time, the electrode pattern 59 is transferredonto the prepreg 57. Then, the prepreg 57 is completely cured.

In step (c), a via hole 62 is formed in the cured resin layer 57 and isthen filled with a conducting material to connect the shield electrode55 with the electrode pattern 59.

As described above, since the shield electrode 55 which functions as theinner layer electrode is included, noise generated from the electroniccomponent mounted another layer in the component-embedded substrate Dand the noise of electromagnetic waves from the exterior are shielded,and satisfactory electrical characteristics are obtained. To achieve asatisfactory shielding effect, the electrode area of the shieldelectrode 55 must be at least about 60% and preferably at least about90% of the single-layer area (the total of the electrode area and thenon-electrode area).

FIG. 6 shows the structure of a component-embedded substrate E accordingto a fifth preferred embodiment of the present invention.

In this preferred embodiment, similar to the component-embeddedsubstrate D, an example in which a shield electrode is included isprovided, except that a shield electrode 70 is provided as the outerlayer electrode.

In this component-embedded substrate E, two resin layers 72 and 73 areprovided with an inner layer electrode 71 provided therebetween, andelectronic components 74 and 75 are connected and fixed onto the frontand back surfaces of the inner layer electrode 71 with conductivebonding materials 76 and 77. The electronic component 74 is a chipcomponent mounted on the inner layer electrode 71 with solder or aconducing adhesive 76. The electronic component 75 is a bare chipmounted on the inner layer electrode 71 with a bump 77. The electrodepattern 71 is connected to a electrode pattern 78 through a via hole 79a. The shield electrode 70 is connected to the inner layer electrode 71through a via hole 79 b.

The component-embedded substrate E is produced by the same process asthat shown in FIG. 4, except that the shield electrode 70 is provided inplace of the electrode pattern 43.

FIG. 7 shows a process for producing a component-embedded substrate Faccording to a sixth preferred embodiment of the present invention. Thisprocess provides an exemplary component-embedded substrate havingthree-layer structure.

Steps (a) to (f) are substantially identical to steps (b) to (h) in thethird preferred embodiment (see FIG. 4). Thus, the same referencenumerals are assigned, and descriptions thereof are omitted.

In step (g), a component-embedded substrate having a two-layer structureis flipped vertically. In step (h), an electronic component 80 isconnected and fixed onto the back surface of the upper-side electrodepattern 36 with a conductive bonding material 81.

In step (i), another supporting layer 83 including an electrode pattern84 provided on a surface thereof is press-bonded onto the surface fixingthe electronic component 80 with a prepreg 82 therebetween. At the sametime, the prepreg 82 is temporarily cured. That is, the prepreg 82 ispress-bonded onto the surface of the first layer prepreg 34, the surfacebeing opposite the surface bonded to the second layer prepreg 41.

In step (j), after thermocompression-bonding and curing the prepreg 82,the supporting layer 83 is separated from the temporarily cured prepreg82.

In step (k), after the temporarily cured prepreg 82 is completely cured,a through hole or via hole 85 is formed in the resin layer 82 and isthen filled with a conducting material to electrically connect thefront- and back-side electrode patterns 36 and 84. Alternatively, theelectrode pattern 84 may be directly connected to the electroniccomponent 80 through the via hole 85.

In this preferred embodiment, the third layer prepreg 82 is laminated onthe surface of the first layer prepreg 34, the surface being oppositethe surface bonded to the second prepreg 41. The reason for this isdescribed below.

After curing the first layer prepreg 34, when the second layer prepreg41 is laminated and cured, the substrate having the two-layer structureis warped toward the second layer prepreg 41 because of the curingcontraction of the second layer prepreg 41.

Accordingly, the third layer prepreg 82 is laminated on the surface ofthe first layer prepreg 34, the surface being opposite the surfacebonded to the second layer prepreg 41. Thereby, the substrate that hasthe two-layer structure and that has been warped toward the second layerprepreg 41 can be warped in the opposite direction because of the curingcontraction of the third layer prepreg 82. As a result, a substratehaving a three-layer structure and having a low warpage is produced.

In the above-described preferred embodiments, the electronic componentsare preferably connected and fixed onto the electrode patterns with theconducting adhesives. Alternatively, solder may be used, and lead-freesolder is preferably used in view of environmental concerns. Forexample, Sn including one to four elements selected from Ag, Bi, Cu, Zn,and In is preferably used.

With respect to the conducting adhesive, a binder that is composed ofepoxy or urethane and that includes Ag, Cu, Ni, Au, Sn, Zn, or Ptserving as a conductive material or a mixture of these may be used.

In the above-described preferred embodiments, the prepreg is temporarilycured before separating the supporting layer, and the prepreg iscompletely cured after separating the supporting layer. Alternatively,the prepreg may be completely cured before separating the supportinglayer.

As is clear from the descriptions above, according to the firstpreferred embodiment of the present invention, a plurality of layers arenot laminated in a single step. By sequentially laminating the prepregsand the electrode patterns, it is possible to produce acomponent-embedded substrate having a multilayer structure.

Therefore, the electrode pattern can be connected to the electroniccomponent with the conductive bonding material. The connectionresistance between the electrode pattern and the electronic component isreduced. The connection reliability is greatly improved.

Furthermore, the inner layer electrode between the prepregs (resinlayers) is a single layer and is different from a structure having twoinner layer electrodes. Therefore, it is unnecessary to contact andelectrically connect the inner layer electrodes to each other.Furthermore, it is possible to prevent the occurrence of delaminationbetween the inner layer electrodes.

The electrode pattern is transferred to the prepreg, and after curingthis prepreg, the next prepreg is laminated. Thus, the first prepreg isnot compressed during every lamination, and there are no problems, suchas the poor electrical connection of the electrical component embeddedin the first prepreg or the deformation of the electrode pattern.

According to the second preferred embodiment, in the case in which theelectronic components are connected onto the front and back surfaces ofthe inner layer electrode, the first electronic component is connectedand fixed onto the surface of the first electrode pattern with theconductive bonding material, and the first electrode pattern istransferred to the prepreg. Then, the second electronic component isconnected and fixed onto the back surface of the first electrode patternwith the conductive bonding material, and another prepreg ispress-bonded onto the back surface of the first electrode pattern.

Therefore, high conduction reliability between the first electrodepattern defining the inner layer electrode and the electronic componentsis achieved and the connection resistance is reduced. As a result, acomponent-embedded substrate having reliable electrical characteristicsis produced.

According to the third preferred embodiment, in the case in which theelectronic components are connected onto the front and back surfaces ofthe inner layer electrode, the supporting layer having the electrodepattern is disposed on the surface opposite the press-bonded surface ofthe prepreg, and then the electrode pattern is transferredsimultaneously with press-bonding. Therefore, in addition to an effectsobtained in the second preferred embodiment, it is unnecessary to form anew electrode pattern after press-bonding the prepreg. Thus, the numberof steps is reduced.

While the present invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically set out anddescribed above. Accordingly, it is intended by the appended claims tocover all modifications of the invention which fall within the truespirit and scope of the invention.

1-7. (canceled)
 8. A process for producing a component-embeddedsubstrate, comprising the steps of: connecting and fixing a firstelectronic component to a first electrode pattern on a first supportinglayer with a conductive bonding material; press-bonding a secondsupporting layer including a second electrode pattern onto theelectronic component-fixed surface of the first supporting layer with afirst prepreg therebetween to perform transfer; separating the firstsupporting layer and the second supporting layer from the first prepregsuch that the first and second electrode patterns are disposed on afront surface and a back surface of the first prepreg; curing the firstprepreg before or after the step of separating the first supportinglayer and the second supporting layer from the first prepreg; connectingand fixing a second electronic component onto a back surface of thesecond electrode pattern with a conductive bonding material;press-bonding a third supporting layer including a third electrodepattern onto a second electronic component-fixed surface with a secondprepreg therebetween to perform transfer; separating the thirdsupporting layer from the second prepreg; and curing the second prepregbefore or after the step of separating the third supporting layer fromthe second prepreg, wherein the prepregs and the electrode patterns aresequentially laminated.
 9. The process for producing thecomponent-embedded substrate according to claim 8, further comprisingthe steps of: forming a through hole in the first prepreg which extendsin a thickness direction of the first prepreg after curing the prepreg;and forming a conducting path inside the through hole, the conductingpath electrically connecting the first and second electrode patternsprovided on the front surface and the back surface of the first prepreg.10. The process for producing the component-embedded substrate accordingto claim 8, further comprising the steps of: forming a through hole inthe first prepreg connecting the electrode pattern provided on the frontsurface or the back surface of the first prepreg with an externalelectrode of the first electronic component after curing the firstprepreg; and forming the conducting path inside the through hole, theconducting path electrically connecting the electrode pattern with theexternal electrode of the first or second electronic component.
 11. Theprocess for producing the component-embedded substrate according toclaim 8, wherein the step of curing the first prepreg further comprisesthe substeps of: performing temporary curing before separating the firstand second supporting layers from the first prepreg; and performingcomplete curing after separating the first and second supporting layersfrom the first prepreg.
 12. The process for producing thecomponent-embedded substrate according to claim 8, wherein the step ofcuring the second prepreg further comprises the substeps of: performingtemporary curing before separating the third supporting layer from thesecond prepreg; and performing complete curing after separating thethird supporting layer from the second prepreg.
 13. The process forproducing the component-embedded substrate according to claim 8, furthercomprising the steps of: press-bonding a fourth supporting layer havinga fourth electrode pattern onto the surface of the first prepreg with athird prepreg therebetween to perform transfer, the surface beingopposite the surface bonded to the second prepreg; separating the fourthsupporting layer from the third prepreg; and curing the third prepregbefore or after the step of separating the fourth supporting layer fromthe third prepreg.
 14. A process for producing a component-embeddedsubstrate, comprising the steps of: connecting and fixing a firstelectronic component on a surface of an electrode pattern on asupporting layer with a conductive bonding material; press-bonding afirst prepreg onto the first electronic component-fixed surface of thesupporting layer; separating the supporting layer from the firstprepreg; curing the first prepreg before or after the step of separatingthe supporting layer from the first prepreg; connecting and fixing asecond electronic component onto a back surface of the electrode patternwith a conductive bonding material; press-bonding a second prepreg ontothe second electronic component-fixed surface; and curing the secondprepreg.
 15. The process for producing the component-embedded substrateaccording to claim 14, wherein the step of curing the first prepregfurther comprises the substeps of: performing temporary curing beforeseparating the supporting layer from the first prepreg; and performingcomplete curing after separating the supporting layer from the firstprepreg.
 16. A process for producing a component-embedded substrate,comprising the steps of: connecting and fixing a first electroniccomponent onto the surface of a first electrode pattern on a firstsupporting layer with a conductive bonding material; press-bonding asecond supporting layer including a second electrode pattern onto theelectronic component-fixed surface of the first supporting layer with afirst prepreg therebetween to perform transfer; separating the firstsupporting layer and the second supporting layer from the first prepregsuch that the first and second electrode patterns are disposed on afront surface and a back surface of the first prepreg; curing the firstprepreg before or after the step of separating the first supportinglayer and the second supporting layer from the first prepreg; connectingand fixing a second electronic component onto the back surface of thefirst electrode pattern with a conductive bonding material;press-bonding a third supporting layer including a third electrodepattern onto a second electronic component-fixed surface with a secondprepreg therebetween to perform transfer; separating the thirdsupporting layer from the second prepreg; and curing the second prepregbefore or after the step of separating the third supporting layer fromthe second prepreg, wherein the prepregs and the electrode patterns aresequentially laminated through the steps.
 17. The process for producingthe component-embedded substrate according to claim 16, furthercomprising the steps of: forming a through hole in the first prepregwhich extends in a thickness direction of the first prepreg after curingthe prepreg; and forming a conducting path inside the through hole, theconducting path electrically connecting the first and second electrodepatterns provided on the front surface and the back surface of the firstprepreg.
 18. The process for producing the component-embedded substrateaccording to claim 16, further comprising the steps of: forming athrough hole connecting the electrode pattern provided on the frontsurface or the back surface of the first prepreg with an externalelectrode of the electronic component after curing the first prepreg;and forming the conducting path inside the through hole, the conductingpath electrically connecting the electrode pattern with the externalelectrode of the electronic component.
 19. The process for producing thecomponent-embedded substrate according to claim 16, wherein the step ofcuring the first prepreg further comprises the substeps of: performingtemporary curing before separating the first and second supportinglayers from the first prepreg; and performing complete curing afterseparating the first and second supporting layers from the firstprepreg.
 20. The process for producing the component-embedded substrateaccording to claim 16, wherein the step of curing the second prepregfurther comprises the substeps of: performing temporary curing beforeseparating the third supporting layer from the second prepreg; andperforming complete curing after separating the third supporting layerfrom the second prepreg.
 21. The process for producing thecomponent-embedded substrate according to claim 16, further comprisingthe steps of: press-bonding a fourth supporting layer having a fourthelectrode pattern onto the surface of the first prepreg with a thirdprepreg therebetween to perform transfer, the surface being opposite thesurface bonded to the second prepreg; separating the fourth supportinglayer from the third prepreg; and curing the prepreg before or after thestep of separating the fourth supporting layer from the third prepreg.